Elastic fluid turbine casing



April 1950 F. c. LINN ELASTIC FLUID TURBINE CASING Filed July 22, 1946.I ll I.

iwN m .5 w 7 5 n A fi F W Fig 2.

Patented Apr. 11, 195

ELASTIC FLUID TURBINE CASING Frank C. Linn, Schenectady, N. Y., assignorto General Electric Company, a corporation of New York Application July22, 1946, Serial No. 685,503

3 Claims.

My invention relates to elastic fluid turbomachines, such as steamturbines, having large and heavy casings divided into halvessubstantially along a diametral plane, particularly to the arrangementof the casing at the high pressure end of such a machine.

While applicable to any such machine in which the inlet temperature ofthe motive fluid is subject to material changes within short periods oftime, it has been found particularly useful in the high pressure end ofthe low pressure cylinder of marine propulsion turbines having more thanone turbine in series flow relation. In such turbines, it is frequentlyrequired, when maneuvering, that the load on the turbine be almostinstantly changed from no-load to full load ahead or full load reverse,and vice versa. Such operation produces an appreciable and varyingtemperature difierential between the steam inlet chest of the turbinecasing and the comparatively cooler portions of the casing including thehorizontal flanges and the shaft seal structures which are radiallyspaced inwardly from the inlet chest. It has been discovered that suchfluctuating temperature gradients cause certain temporary warpage of thecasing halves, with the result that the joint between the sectionsdistorts sufliciently to permit a small amount of leakage between theflanges. The steam is at or near its dew point and therefore may erodethe surfaces of the easing joint. This resulting erosion increases withtime unless corrective measures are taken. Because of the difliculty andcost of disassembling the turbine in a marine powerplant for repair ofthe horizontal joint flanges, and the resulting loss of utilization ofthe ship, it is imperative that such partial top view taken on the plane33 of Fig. 2,

showing the arrangement of the horizontal flanges which secure togetherthe two halves of the turtegral with the two halves of the casing is asteam leakage and erosion :be eliminated or reduced to a minimum.

The object of my invention is to provide an improved casing arrangementfor the high pressure end of a large heavy turbine casing of the typedescribed which eliminates the above-mentioned leakage difllculties,which may be encountered with pre-existing designs.

Other objects and advantages will be apparent from the followingdescription taken in connection with the accompanying drawings, in whichFig. 1 is a vertical section through the axis of a turbine with a casingincorporating my invention; Fig. 2 is a partial end view of the turbinecasing taken on the irregular plane 22; and Fig. 3 is a inlet chest I.As shown in the drawing the steam chest is provided in both halves ofthe casing, extending completely around the casing adjacent to the firststage bucket-wheel 8. It will of course be obvious to those skilled inthe art that my invention is equally applicable to turbines havingpartial arc admission in the first stage, in which event the steam inletchest I may be provided in only one section of the turbine casing.Supported in the turbine casing in cooperating relation with the inletchest I is a ring 9 defining a plurality of circumferentially spacednozzles l0 adapted to supply motive fluid to the buckets of the firststage wheel 8.

The shaft I is supported in a suitable bearing indicated generally at H,the structural details of which are not essential to an understanding ofthe present invention. Surrounding shaft i is a packing assembly l2including a number of axially spaced packings consisting of segments l3of soft metal or carbon arranged to be biased into sealing engagementwith the shaft by suitable springs I4 which engage the respectivesegments [3. Packings of this general type are well known in the art andfurther mechanical details are also believed unnecessary to anunderstanding of the present-invention.

As will be understood by those familiar with steam turbines for marinepropulsion, the casing halves of such machines are massive units formedwith heavy sections to withstand the forces involved without detrimentaldistortion under the severe conditions encountered in marine service.For instance, the inlet end of the casing, as represented in Fig. 1, maybe of the order of 5 feet in outside diameter; while the exhaust end(not shown) may be of the order I! feet in outside diameter. One half ofsuch a casing may weigh between 5,000 and 10,000 pounds.

The casings represented in the drawings may be fabricated by weldingfrom rolled or forged steel sections. It will of course be understoodthat my invention is also applicable to cast casings.

It will be observed in Fig. 1 that the steam chest 1 is radially spacedfrom the shaft packing assembly II. For low load operation of the lowpressure element of a marine turbine of the type described, thetemperature of the metal walls of chest 1 may be of the order of 300 F.,while the shaft and packing may be at about 240 F. Normally in starting,the turbine will be operated at low load until all parts of the turbinereach their respective steady state temperatures. However, at certaintimes, as when leaving the dock,

it is necessary to instantaneously increase the turbine load to its fullrated value or nearly so. As a result, the temperature of the inletchest I may quickly rise to the neighborhood of 400 F.,

while the portions of the casing radially inward from the steam chestmay remain at about 250 F. If the turbine continues to operate at fullload or thereabouts, a new steady state temperature level will bereached at the end of about one hour's time, when the parts in theneighborhood of the shaft seal and bearing assemblies may be in theneighborhood of 335 F. This differential (as compared with the 400 inletchest temperature) may be sufficient to produce opening of thehorizontal flange to allow continuous steam leakage which will result inprogressively increasing erosion. The above-described transienttemperature differential occurring when the load is suddenly changedfrom minimum to maximum of course produces a similar efiect to a greaterdegree.

I have found that the leakage difficulties heretofore experienced withthe massive casings ordinarily used can be completely eliminated by theinterposition of a flexible casing section between the comparatively hotinlet chest 1 and the cooler shaft region with its seal and bearingassemblies H, II. In Fig. 1 this flexible section is indicated at I 5.It comprises a ring member of thin fiat cross-section which is dishedinwardly in an axial direction and extends from the inner casing ringmember l6 radially outward to the ring 11, the latter being welded tothe inlet chest I in a manner which may be seen in Fig. 3.

In 'Fig. 2 can be seen a plan view of the flexible ring and its relationto the inner and outer rings l6, l1 and flange to which it is welded.Also shown are two of the bolts which secure the casing halves together.It will be understood that a row of studs I8 are secured in the flange2| of the lower casing half, nuts 19 serving to force the flange 20 ofthe upper easing into tight sealing engagement with the flange 21 of thelower casing. The plane mating surfaces of these flanges are carefullyfinished so as to provide a steam tight seal when the flanges areclamped together by the threaded fastenings I 8, l9. To provide asufficiently tight fit, the studs 18 may first be heated with ablow-torch and then the nuts I! assembled and tightened down firmly. Theensuing shrinkage of studs I8 as they cool will produce veryconsiderable forces to hold the casing halves together.

As may be seen in Fig. 3, by arranging the curved ring I i so that itbows inwardly (that is,

is concave as viewed from the outside of the cas ing), additional roomis provided on the flange 20 for locating an additional stud Ma. Theline of action of the force provided by this stud lid is substantiallyin the plane of the rings l5, l1 and therefore provides particularlyeffective sealing engagement between flanges 20, 2| immediately adjacentthe shaft seal assembly II. This is an important advantage of myarrangement, for leakage through the casing joint at thi point has beenparticularly troublesome.

With my invention it has been found that the massive casings forturbines of the type described can be readily manufactured so as to becompletely leakproof at the casing joint over long periods of exactingservice in marine powerplant installations.

While my invention has been described as applied to a steam turbine formarine propulsion powerplants, it may also flnd utility in analogouscasings of other turbo-machines, such as multistage axial fiowcompressors, etc.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is:

1. An elastic fluid turbo-machine subject to rapid and material changesin temperature of the operating medium comprising a casing having aradially extending end wall portion thereof divided into at least twosections along an axial plane with joint flanges around the periphery ofthe respective sections, fastening means clamping the joint flangestogether, and rotor shaft sealing means supported by said end wallportion, the high temperature end of the casing forming a hightemperature fluid chamber radially spaced from the shaft seal means,said casing end wall having a radially inner portion connected to theshaft seal means and an outer circumferential portion connected to theradially inner wall portion of the high temperature fluid chamber andincluding a thin-walled portion having a cross section forming a simplearcuate curve bowed inwardly relative to the casing so as to haveappreciable flexibility in a radial direction, whereby differentialthermal expansion of the high temperature chamber relative to the shaftseal means may take place without distortion of the casing section atthe dividing plane therebetween, the inwardly curved flexible sectionproviding maximum available space for the fastening means on the jointflanges, a part of said flange clamping means being located immediatelyadjacent the shaft seal means with the line of action thereof lyingsubstantially in the plane of the casing end wall portions to which theflexible section is connected.

2. An elastic fluid turbo-machine subject to rapid and material changesin temperature of the operating medium comprising a casing having aradially extending end wall portion divided into at least two sectionsalong an axial plane with joint flanges around the periphery of therespective sections, fastening means clamping the joint flangestogether, rotor shaft sealing means supported by the casing end wallportions, the end of the casing adjacent said radially extending wallportion forming a high temperature fluid chamber radially spaced fromthe shaft seal means, said casing end wall having a radially innerportion connected to the shaft seal means and an outer circumferentialportion connected to the radially inner wall of the high temperaturefluid chamber and including a thin-walled portion of curvedcross-section having appreciable flexibility in a radial direction,whereby 8,508,014 7 5 I 6 limited differential thermal expansion or thefluid chamber walls relative to the shaft seal means REFERENCES CITEDmay occur without distortion of the casing The following references areof record in the tions at the axial dividing plane therebetween me ofthis patent:

3. An elastic fluid turbo-machine casing ar- 5 UNITED STATES PATENTS,

rangement in accordance with claim 2 in which the curved flexiblesection is bowed inwardly so i 5 ggg: P

as to appear concave from the exterior or the 167o'452 Kaehler f y- 19283851118, whereby maximum o ting space is made 6 Lysholm M 1 37 availablen the flanges immediatel adjacent thg o v shaft seal means. A

FRANK C. LINN.

